10
5.
The bath is not heating when it should be
requesting heat. Voltage measurements are
made on the POWER SUPPLY BOARD
#3166924.
a. Select a setpoint temperature at least
10°above what the actual temperature is.
The bath should be requesting heat as
indicated by the heater "ON" indicator
lamp on the front panel. It should be on
continuously, not flashing.
b. Measure the voltage at U1-PIN 2 with
respect to TP2-COM. It should be no
greater than 4 VDC.
c. Measure the DC voltage across R4. Since
the bath is requesting heat, there should
be current flowing through this resistor
making the voltage drop equal to 3 vdc
±0.5.
d. If the last two steps are not as stated, then
most likely the CPU board is bad and it will
have to be replaced.
e. Switch the voltmeter to an AC volts scale
capable of reading 120 volts.
f.
Measure the voltage between U1-PIN 4
and U1-PIN 6. It should be less than 1
VAC.
g. If it is not, then most likely the opto-coupler
U1 is bad and the POWER SUPPLY board
will have to be replaced. If it is, continue
on.
h. Measure the voltage directly across the
heater. It should be line voltage 110VAC
to 120 VAC.
Open the control cover and familiarize yourself
with the POWER SUPPLY assembly #3166924.
Locate the triac (Q2), the opto-isolater (U1), the
resistor (R4), and the test point #2 (TP2-COM).
The first measurements will be DC voltage
measurements. A DC scale of at least 10 volts
should be selected.
PROBLEMS & SOLUTIONS
*********** Problem A : No Heat *************
1.
Verify that the setpoint temperature is greater
than the actual water temperature.
2.
Verify that the HIGH TEMP light is "OFF". If
the light is "ON", turn the HIGH LIMIT
CONTROL fully clockwise.
3.
Check temperature probe voltage reference.
These measurements are on the CPU board
#3167119.
a. Place the negative lead of a DC voltmeter
on TP1-COM test point. Measure the
voltage at U7-pin 2. It should be
approximately 14 volts DC. Now measure
the voltage at U7-Pin 6. It should be
approximately 5 volts DC. If the 14 volts is
present but not the 5 volts, the CPU board
must be replaced.
4.
Check temperature probe.
a. Measure the bath water temperature and
make note of it. Make sure it will not
change drastically during this check.
b. With a DC voltmeter, measure the supply
of the temperature sensor at J302 pins 1 &
3. It should be approximately 5 volts. If it
is, then continue on to step C. If not, see
Step 3a.
c. Measure the output of the temperature
sensor at J302 pins 2 & 3. Pin 3 being the
reference or ground. The output
relationship of voltage to degrees
centigrade is listed in the table below.
Compare the measured voltage to the
temperatures listed to determine if the
probe is working.
Temp
Degrees C
Volt
Temp
Degrees C
Volt
10
0.500V
60
1.400V
20
0.680V
70
1.580V
30
0.860V
80
1.760V
40
1.040V
90
1.940V
50
1.220V
99
2.218V
